Planar tube



March 19, l

E. T. PENNINGTON PLANAR TUBE Filed Aug. 30, 19 1 INVENTOR fdgar 7. Fem/71g fa/z Maw ATTORNEY 3,082,348 Patented Mar. 19, 1963 fifice ware Filed Aug. 30, 1961, Ser. No. 142,996 4 Claims. (Cl. 313-250) This invention relates to electron tubes of the planar type wherein electrode elements having plane faces are stacked within an envelope with the faces parallel to one another.

An object of this invention is to provide an improved support for the cathode employed in the tube whereby, notwithstanding changes in dimensions thereof due to heating, the distance between the active face of the cathode and the adjacent electrode face remains relatively unchanged.

Most ceramic planar tubes comprise stacked layers of components. Enclosure and brazing together of the layers must be done within a vacuum, as within an evacuated bell jar. This type of construction requires individual handling of the tubes and prevents exhausting and further treat-ment of the tube in conventional automatic turret type machinery.

Other planar tubes involve the use of a large metal base. This structure permits exhausting of the tube on either trolley or turret exhaust systems but has the disadvantages of making the tube size large and the interelectrode capacitances high. The structural configuration also limits the cavity characteristics both as to operable frequency and tube compactness.

It is, therefore, another object of the invention to provide a planar tube construction which may be assembled and exhausted on conventional exhausting equipment and yet be rugged and diametrically compact.

Other objects of the invention will become apparent upon consideration of the following description when taken in conjunction with the accompanying drawings in which:

FIG. 1 discloses a vertical cross' section through the improved planar tube; and

FIG. 2 is a top view of a ceramic spacer annulus.

Referring to the drawing, the reference character indicates a ceramic or glass dome rigidly mounting an anode 12 having a lower plane face 14. The anode has a vertical passageway 16 therethrough in which is secured an exhaust tube 18, of metal or glass, as desired. This exhaust tube is tipped off or sealed as seen at 19' in the drawing after the electron tube had been exhausted through the exhaust tube. The lower end of the vertical passageway 16 communicates with a horizontal bore 20 leading to the space within the ceramic or glass dome 10.

Brazed or otherwise hermetically sealed to the glass dome is a metallic grid washer 22 spaced from the anode. This washer extends annularly within the dome and also likewise extends exteriorly thereof. Electrical connection may be made to the exterior portion of the grid washer at any point desired. Hermetically sealed to the lower face of the grid washer is a ceramic or glass cylinder 24 of a thickness and outside diameter equal to that of the lower end of the dome. The inner annular extension of the grid washer affords a seat or shelf 25 for a grid 26, the metallic frame 28 of the grid bearing against the under surface of the metallic washer to be in electrical contact therewith. Grid wires 30 span the grid frame and are fastened thereto. The under surface of the grid washer 22 may be considered as a reference level for spacing of electrode elements from each other; the lower surface of the anode may be close to this reference level although this spacing depends on the electrical characteristics desired.

The spacing between the grid wires 30 and the top of the cathode, however, is critical. To attain this desired spacing, there is placed against the under surface of the grid frame a spacing member or foil ring 32, as thin as desired to attain the desired spacing between grid wires and cathode. Bearing against the foil ring is an insulating annulus 34, as of ceramic. The annulus may have three annular projections 36, as shown in FIG. 2, against the under side of which bear lateral projections shown, for example, as an annular bead 38 of an inverted cathode cup 40. The top wall 42 of the cup on its outer surface is coated with the electron emissive material 44. Cooperating with the spacer annulus and the bead 38 is a ceramic cylinder 4-6 having projections 48 mating with the projections 36 on the annulus 34 and serving to clamp the bead 38 of the cathode cup between the annulus and the cylinder 46. Since the head 38 is close to the upper end of the inverted cup, thermal expansion in the cathode is predominantly below this point and so there is negligible effect on the spacing between grid and cathode. Urging the cylinder '46 upwardly is an expansive tensioning element 48; in this embodiment a coiled spring is shown reacting between the bottom annular wall of the cylinder 46 and a ceramic or glass washer 49 hermetically sealed and fastened to an inside flanged base ring 50. The lower edge of the ring is hermetically fastened, by welding, brazing, or the like, to an outside flanged ring 52 in turn fastened to the lower edge of cylinder 24 and hermetically sealed with respect thereto. The ring 52 is substantially at the periphery of the base of the envelope.

The cathode includes a coiled heater 54, the ends of which insulatively pass through a heat reflector plate 58 such as passive nickel having a flange 59 welded to the interior of the cathode cup surface. Current is fed to the heater through ends 62, thence through rods 64, soldered into hollow terminals 66 hermetically sealed within the bottom ceramic 49. Although a tab may be affixed to the cathode cup and connected with the outside bottom ring 52 to provide an electrical connection for the cathode, it is preferred to coat three localized areas of the ceramic cylinder 46 with vertical strips of conductive film 68. These areas immediately surround the three projections 36 and extend perpendicularly downward along the inside of the cylinder 45 so that when the cylinder is pressed up against the bead 38 on the cathode cup by the spring 48, a good electrical contact is secured between the cathode cup and the conductive films. The film strips 68 are electrically joined to an annular ring 69' of like conductive material bonded to the under surface of cylinder 46.

The tensioning element or spring 43 is in pressured contact with conductive ring 69 at the top and in similar contact with ceramic 49 at the bottom. Bottom ceramic 49 has bonded to its circumferential edge and adjacent peripheral areas an annular tire of electrically conductive material 71. Thus spring 48 serves as an electrical link in the cathode conductor. Spring 49 being, in this instance, in the form of a helix is apt to produce the inductance of a coil in high frequency operation. To avoid the resultant unwanted inductive field, several light metal shorting tabs 70, as of nickel or the like, are placed equidistantly around the periphery of the spring and welded thereby electrically joining the top and bottom coils. The cathode connection is completed by brazing conductive material 71, on the bottom ceramic 49, to inside base ring 50. The connections thus provided for the heater and cathode results in extremely small interelectrode capacitance.

The tube may be assembled by first associating the 3 dome 10 with its anode 12 and exhaust tube 18, the tube now not yet being pinched off. The dome is further associated with its grid washer 22 and cylinder 24 with its ring 52.

Next the assembled and united anode, dome, washer, and cylinder are inverted and a number of parts are insorted into the cylinder. First the grid 26 is seated against the annular internal projection of the grid Washer 22 with the grid wires 30 uppermost. Next the ring foil 32 is inserted, this being of the thickness required to give the desired spacing between the wires on the grid frame and the electron emissive coating on the cathode cup. After this, the spacer annulus 34 is inserted and next the cathode assembly. The cathode assembly includes the cathode cup 40 coated with electron emissive material 44 on the exterior of its planar wall, the reflector plate 58, the heater 54, and rods 64.

After all these parts have been assembled, the cylinder 46, with its integrated conductor 68 and 69 is dropped into place. The spring 48, with its shorting tabs, is then located against the conductive material 69' on cylinder 46. Finally, the bottom assembly comprising bottom ceramic 49 positioned inside ring 50 and terminals 66 is placed in position. In the placing of the bottom assembly, the heater rods 64 are first threaded through the terminals 66 and then the bottom assembly is thrust to proper position against the action of spring 48. While so held, the two rings 50 and 52 are brazed or welded together in airtight relationship. The heater rods 64 are next adjusted in position relative to the terminals 66, and the two are dip-soldered or brazed together, as is common in the art. The dome and cylinder sections 10, 24 of the tube, and the bottom ceramic 49, form the enevelope for housing the electrode elements.

The completely assembled tube may now be mounted on an exhaust machine with the tube 18 connected to an exhaust port of the machine and the tube evacuated. When properly evacuated, the tube is tipped off, thus completing the exhausting of the tube.

Although several embodiments of the invention have been described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

Having thus described the invention, what is claimed 1. A planar tube including an envelope enclosing an anode, a grid, and a cathode, means for supporting said cathode in spaced relationship to the grid comprising an annular shelf within the envelope, a grid seated against said shelf, a spacing member bearing against the grid and an insulating annulus bearing against the member, said annulus having projections extending toward the center of the annulus, said cathode having a lateral extension near its upper end underlying the projections on the annulus, an insulating cylinder having projections similar to those on the annulus engaging the lateral extension on the cathode, and a spring within the envelope and acting against the insulating cylinder to hold the cathode in proper position within the envelope.

2. The subject matter of claim 1 wherein the cathode is in the form of an inverted cup and there is a heater having terminal pins mounted within the cup, wherein the bottom of the cup is closed off with a heat reflecting plate, with the terminal pins extending through the reflector plate.

3. The subject matter of claim 1 wherein a connection is made to the cathode by conductively coating at least one (preferably all) of the extensions on the cylinder so that it comes into contact with the lateral extension on the cathode and wherein said coating is electrically connected to a conductive ring attached to the bottom of the envelope.

4. A planar tube including an envelope enclosing an anode, a grid and a cathode having a laterally extending projection, said anode extending upwardly from the tube and affording electrical connection to the tube at the top of the tube, a grid washer extending through the envelope having a portion external of the tube to which electrical connection may be made, said washer having an internal annular shelf, a grid seated against said shelf and in electrical contact therewith, a cylindrical insulating member having projections extending toward the cathode and underlying the projections on the cathode, an electrical-conducting medium between the extensions and extending partially along the interior wall of the cylinder making electrical contact with the spring, a bottom ceramic with peripheral conductive material contacting the bottom end of the spring, a shorting means for the spring, a conductive ring at the periphery of the base of the envelope completing the cathode connection, a heater within the cathode, and leads to the heater extending through the base of the envelope substantially centrally of the base.

No references cited. 

1. A PLANAR TUBE INCLUDING AN ENVELOPE ENCLOSING AN ANODE, A GRID, AND A CATHODE, MEANS FOR SUPPORTING SAID CATHODE IN SPACED RELATIONSHIP TO THE GRID COMPRISING AN ANNULAR SHELF WITHIN THE ENVELOPE, A GRID SEATED AGAINST SAID SHELF, A SPACING MEMBER BEARING AGAINST THE GRID AND AN INSULATING ANNULUS BEARING AGAINST THE MEMBER, SAID ANNULUS HAVING PROJECTIONS EXTENDING TOWARD THE CENTER OF THE ANNULUS, SAID CATHODE HAVING A LATERAL EXTENSION NEAR ITS UPPER END UNDERLYING THE PROJECTIONS ON THE AN- 